It really depends on the kind of fire extinguisher as to whether that matters. That said, my understanding is that if it is a dry powder that has settled it would be visible on the pressure gauge.
Really, that is about actually checking the pressure gauge every six months. If you tell someone to look, they never will. If you tell someone they have to do something, they might. Its the same logic behind “testing” a smoke alarm. The electronics are simple enough that you would REALLY need to try to damage them (and they are set up to piss you off with incessant beeping when failing anyway). But by pushing the button every six months, you actually check if there is a battery in it and so forth. Rather than hearing it beep in the morning, telling yourself you’ll fix it when you get home, and never doing so.